This project will seek to characterize attentional and inhibitory dysfunction in PTSD using innovative psychological and neuroimaging methods, and will focus on a central unanswered question: are increased attentional/inhibitory failures in PTSD driven by an inability to consistently engage task-positive cognitive control networks of the brain, or rather are they due to inappropriate engagement of task-negative brain networks associated with distraction? Thus, this project will identify the neural networks responsible for attentional disruption in PTSD, by using spatiotemporal patterns of brain activity to predict attentional lapses in real time, as well as to predict clinical diagnosis and severity. The proposal systematically explores sustained attention and inhibitory control in the context of fearful stimuli, as well as in more neutral, everyday contexts, using novel behavioral and fMRI methods developed by the principal investigator. This characterization of attentional and inhibitory control in PTSD will help explain difficulties that these individuals have in everyday life, and will be translatable to therapeutic augmentation and improved neurocognitive-based interventions. The project will also provide training in neuropsychological, psychiatric, and neuroimaging aspects of PTSD. This will facilitate the applicant's career goal to become a full-time, fully-funded independent investigator researching the neurocognitive injuries facing veterans, and allow the applicant to assume a leadership role as a VA scientist and to help train the next generation of researchers. The applicant is wholly committed to expanding his skills to better the lives of veterans. He intends to continue his career within the VA indefinitely. DESIGN: First, the project consists of a task-based fMRI experiment, which investigates the neural signature of sustained attention and inhibitory control deficits in individuals with PTSD. Participants (n=96) will be drawn from a RR&D TBI Center of Excellence at VA Boston- a large, extremely well-behaviorally characterized sample of OEF/OIF veterans with varying degrees of PTSD. Second, the project includes functional connectivity analyses of resting fMRI data, including multivariate pattern analyses, in an expanded set of individuals from the TBI Center. METHODS: The first set of experiments uses a novel continuous performance task and concurrent fMRI, in order to assess sustained attention and inhibitory control, and the effects of both affective and non-affective distractions. Second, an expanded cohort of participants will undergo MRI scans to examine resting state functional connectivity in core attentional and inhibitory control networks of the brain. Pattern classification (decoding) models of functional connectivity will potentially reveal neurobiological markers of PTSD. OBJECTIVES: Aim 1. Neurally and behaviorally characterize sustained attention and inhibitory deficits in PTSD. Hypothesis 1A. Sustained attention deficits in PTSD+ vs. PTSD- will be exacerbated by distraction, and emotional distraction in particular (neutral and fearful faces). Hypothesis 1B. Sustained attention deficits in PTSD+ vs. PTSD- will be characterized by increased distraction (distraction model) as reflected by inappropriate engagement of the default mode network (mind-wandering) and face-specific brain regions associated with neutral face distractors, and in particular, fearful face distractors. Hypothesis 1C. Independent of distraction, sustained attention deficits in PTSD+ vs. PTSD- will be characterized by failure to consistently engage task- positive brain networks, including the salience and dorsal attention networks (depletion model). Aim 2. Examine PTSD-related alterations in intrinsic functional brain connectivity, using multivariate pattern analysis (MVPA). Hypothesis 2. PTSD will be associated with abnormal connectivity in the 1) Salience network and 2) Dorsal attention network, associated with attentional, inhibitory and emotional control and 3) Default mode network, associated with mind-wandering and task-unrelated thoughts. These connectivity patterns will reliably predict the presence and severity of PTSD.